It is often desirable to provide a coupling between the rotating output of a prime mover and the rotating input of a driven load that permits a disparity between the rotational speed of the rotating output of the prime mover and the rotating input of the driven load. For example, in order to permit continuous rotation of the output of the prime mover, even when it is desirable to stop rotation of the input of the driven load, it is desirable to provide a coupling that permits the rotational output of the prime mover to continue despite the input of the driven load being stopped.
An example of such a coupling is a torque converter, which provides a hydrodynamic fluid coupling between the rotating output of a prime mover and the rotating input of a driven load. For example, a machine such as a vehicle may include an internal combustion engine and a transmission, with the output of the internal combustion engine coupled to an input of the transmission by the torque converter.
A torque converter generally includes an input coupling for coupling the output of a prime mover to the input of the torque converter, and an output shaft for coupling the output of the torque converter to a driven load, such as a transmission. A torque converter further includes a housing containing fluid, such as hydraulic fluid. Within the housing, the input coupling is coupled to a pump including an impeller for pumping the fluid in the housing. A torque converter further includes a turbine coupled to the output shaft of the torque converter. The impeller of the pump, driven by the input coupling, pumps fluid through the turbine, thereby causing the turbine to rotate and drive the output shaft of the torque converter and the input of, for example, a transmission. By virtue of the fluid coupling provided by the interaction between the impeller and the turbine, the output of the prime mover may continue to rotate the input coupling of the torque converter, even when the output shaft of the torque converter is stopped.
In some situations, it may be desirable to bypass the hydrodynamic fluid coupling between the impeller and the turbine to improve the efficiency of the torque transfer from the prime mover to the output shaft of the torque converter. For example, when the turbine reaches, for example, about 90% or more of the rotational speed of the impeller due to the hydrodynamic interaction between the turbine and impeller, the hydrodynamic coupling may become less efficient than a mechanical coupling between the prime mover and the output shaft of the torque converter. In addition, at such relative speeds, it may no longer be desirable to provide for a relative disparity of rotational speeds between the prime mover and the output shaft of the torque converter.
To improve efficiency, some torque converters include a lock-up clutch that, when activated, bypasses the hydrodynamic fluid coupling and provides a mechanical coupling between the prime mover and the output shaft of the torque converter. For example, a lock-up clutch may include a clutch housing mechanically coupled to the prime mover and friction members mechanically coupling the clutch housing to the output shaft the torque converter. Upon engagement of the lock-up clutch, interaction between the friction members transfers torque between the clutch housing and the output shaft of the torque converter.
Conventional lock-up clutches may suffer from a number of potential drawbacks. For example, the torque transfer capacity of the lock-up clutch is limited by the interaction between the friction members. The interaction between the friction members may be provided by pressing the friction members together, which may be accomplished using pressurized fluid supplied by the torque converter. However, the pressure of the fluid is limited, and thus, the torque carrying capacity of the torque converter may be limited by the fluid pressure. As a result, it may be desirable to provide a lock-up clutch having a higher torque carrying capacity for a given fluid pressure available from the torque converter. Further, it may be desirable to improve the operation of a torque converter while reducing its complexity and/or cost.
An example of a torque converter having a lock-up clutch is described in U.S. Pat. No. 5,964,329 to Kawaguchi et al. (“the '329 patent”). In particular, the '329 patent discloses a lock-up mechanism in a torque converter that includes a clutch portion capable of selective engagement and disengagement between a front cover and a turbine. A piston member forms a sealed oil chamber together with the front cover and selectively engages and disengages the clutch portion in accordance with the change in the oil pressure within the oil chamber.
Although the '329 patent discloses a torque converter having a lock-up clutch to provide a mechanical coupling between the front cover and the turbine, it may suffer from a number of possible drawbacks. For example, the mechanical coupling disclosed in the '329 patent may not be capable of transferring high torque loads between a prime mover and an output shaft of the torque converter due to the design of the lock-up clutch. The assembly and method disclosed herein may be directed to mitigating or overcoming this and other possible drawbacks.